double refraction refraction in which incident rays are divided into two refracted rays.

dynamic refraction refraction of the eye during accommodation.

ocular refraction the refraction of light produced by the media of the normal eye and resulting in the focusing of images upon the retina.

static refraction refraction of the eye when its accommodation is paralyzed.

re·frac·tion

(rē-frak'shŭn),

1. The deflection of a ray of light when it passes from one medium into another of different optic density; in passing from a denser into a rarer medium it is deflected away from a line perpendicular to the surface of the refracting medium; in passing from a rarer to a denser medium it is bent toward this perpendicular line.

2. The act of determining the nature and degree of the refractive errors in the eye and correction of the same by lenses.

refraction

1. the act or process of refracting; specifically, the determination of the refractive errors of the eye and their correction with lenses.

Refraction by the eye in (A) emmetropia; (B) hyperopia; and (C) myopia.

2. the deviation of light in passing obliquely from one medium to another of different density.refrac´tive

double refraction refraction in which incident rays are divided into two refracted rays, so as to produce a double image.

dynamic refraction the normal accommodation of the eye which is continually exerted without conscious effort.

refraction

(rĭ-frăk′shən)

n.

1. The deflection of a wave, such as a light or sound wave, when it passes obliquely from one medium into another having a different index of refraction.

2. Medicine

a. The ability of the eye to bend light so that an image is focused on the retina.

b. Determination of this ability in an eye.

re·frac′tion·al, re·frac′tive adj.

re·frac′tive·ly adv.

re·frac′tive·ness, re′frac·tiv′i·ty(rē′frăk-tĭv′ĭ-tē) n.

refraction

[rifrak′shən]

Etymology: L, refringere, to break apart

1n, the change of direction of energy as it passes from one medium to another of different density.

2n, an examination to determine and correct refractive errors of the eye.

3n, (in ultrasonography) the phenomenon of bending wave fronts as the acoustic energy propagates from the medium of one acoustic velocity to a second medium of differing acoustic velocity.

4adj, pertaining to the recovery period after an action potential either in muscular or nervous tissue. refractive, adj.

refraction

OphthalmologyThe determination of the optical state of the eye and the basis for prescribing glasses and contact lenses.

OpticsThe alteration of a light wave when it passes from one medium to another—e.g., from a lens to water.

re·frac·tion

(rē-frak'shŭn)

1. The deflection of a ray of light when it passes from one medium into another of different optic density; in passing from a denser into a rarer medium, it is deflected away from a line perpendicular to the surface of the refracting medium; in passing from a rarer to a denser medium, it is bent toward this perpendicular line.

2. The act of determining the nature and degree of the refractive errors in the eye and correction of them by lenses. Synonym(s): refringence.

refraction

1. The bending of light rays that occurs when they pass obliquely from a transparent medium of one density to one of another density.

2. The assessment of the optical errors of the eyes so that appropriate correcting spectacles can be prescribed.

Refraction

The bending of light rays as they pass from one medium through another. Used to describe the action of the cornea and lens on light rays as they enter they eye. Also used to describe the determination and measurement of the eye's focusing system by an optometrist or ophthalmologist.

refraction

; refringence radiation divergence as it passes between media of different densities or across an interface

refraction

1. The change in direction of the path of light as it passes obliquely from one medium to another having a different index of refraction (Fig. R7).

2. The process of measuring and correcting the refractive error of the eyes. Syn. refraction of the eye; sight testing (obsolete term).

3.Seerefractive error. Seelaw of refraction.angle of refraction Seeangle of refraction.binocular refraction A clinical procedure in which the subjective measurement of refraction of each eye is performed while both eyes are viewing a test. The visual examination is thus carried out under more natural conditions than when one eye is closed; the sizes of the pupils are similar and the accommodation-convergence relationship is maintained. There are various such methods; using polarized targets (e.g. Vectograph slides; Parallel-testing Infinity Balance test), using a septum (e.g. Turville Infinity Balance test), or fogging (e.g. Humphriss Immediate Contrast test). These methods give better results than refracting monocularly, especially in latent hyperopia, hyperopic anisometropia, pseudomyopia, cyclophoria, etc. and no additional step for binocular balancing is necessary. SeeHumphriss method; balancing test; infinity balance Turville test; testing in parallel.cycloplegic refraction Assessment of the refract-ive state of the eye when accommodation has been totally or partially paralysed by a cycloplegic (e.g. cyclopentolate 1% eyedrops, or atropine 0.5 or 1% ointment). This may be carried out in children to reveal the full extent of a hyperopia or in the initial assessment of accommodative esotropia, but only occasionally in adults as fogging methods usually suffice for them. Seecycloplegia; accommodative strabismus.double refraction The splitting of an incident ray into two (ordinary and extraordinary) by a birefringent medium. Seeanisotropic; birefringence; Nicol prism; Wollaston prism.dynamic refraction Determination of the refract-ive state of the eye when accommodation is stimulated, as distinguished from static refraction which is the determination of the refractive state of the eye when accommodation is at rest or paralysed. Seerefractive error; dynamic retinoscopy.error of refractionSeeametropia; refractive error.refraction of the eye1.See refraction.

2. Refraction of light by the optical media of the eye.

3.Syn. for ametropia. Seeametropia; refractive error.index of refractionSeeindex of refraction.laser refraction A method of subjective refraction in which the patient observes a slowly rotating drum, on the surface of which is perceived a speckle pattern resulting from illumination by a laser. The speckle pattern appears to move only when the eye is not focused for the fixation distance. If the perceived movement of the pattern is opposite to that of the drum, the eye is myopic and if the perceived movement of the pattern is in the same direction as the drum, the eye is hyperopic. Correction can be determined by placing a lens in front of the eye, which will neutralize the movement; at that point the eye is focused for the fixation distance. Astigmatism can be measured by rotating the drum in various meridians. The drum can be placed at infinity or at near (an allowance for the radius of curvature of the drum and the distance must then be made). This method can be useful for mass screening, especially children, as accommodation is not stimulated as much as with Snellen letters. It has been very useful as a research tool for accommodation studies where it is arranged as part of a Badal optometer.manifest refraction The refractive error or the process of determining it, when accommodation is at rest (but not paralysed). Seecycloplegic refraction.objective refraction Measurement of the refraction of the eye that is not based on the patient's judgements, as when using an objective optometer or a retinoscope. Seephotorefraction.static refractionSeedynamic refraction; refract-ive error.subjective refraction Measurement of the refraction of the eye based on the patient's judgements. Seefogging method; optometer; duochrome test; fan and block test; plus 1.00 D blur test.

Fig. R7Refraction of light from water into air. Object O forms an image at O′ which appears closer to the surface than it actually is. Thus the apparent thickness t′ of a pool of water (or block of glass), in air, is smaller than its true thickness t and the greater the index of refraction n, the smaller it appears, i.e

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